This invention relates in general to cushioning devices, particularly to cushions having a plurality of inflatable cells, and specifically to cushions having a series of cells formed from a thermoplastic polymer.
Conventional cushioning devices for supporting the human body, such as the typical mattress, seat cushion or padded back rest, do not distribute the weight of the supported body evenly over the area of the body that is in contact with the cushioning device. For example, in the case of a mattress, the buttocks or hips, and likewise the shoulders, sink further into the mattress than the lumbar region of the back. Since most conventional cushioning devices exert a supporting force that is proportional to the amount they are deflected, those portions of the body which sink deepest into the cushioning device experience a resisting force per unit area that is considerably greater than those body portions that deflect the cushioning device only slightly. For those individuals who are confined to beds or wheelchairs for extended periods of time the unequal distribution of supporting forces deforms the vascular system and reduces blood flow which can lead to extreme discomfort and can even be debilitating in the sense that bed sores often develop at the skin areas where the supporting force is greatest.
While cushions which derive their cushioning properties from inner springs or foam material are quite common and inexpensive to manufacture, they suffer the inability to distribute loads or develop restoring forces evenly to the object they are supporting.
I have patents which relate to cushions which have upstanding interconnected air cells which distribute the supporting forces more evenly and indeed generally uniformly over the entire supported area. These cushions employ a series of air cells which are extended generally perpendicular from a base and are, therefore, oriented generally perpendicular to the contacting surface of the body that they support. Moreover, all of the cells are interconnected and, therefore, exist at the same internal pressure irrespective of the extent of deflection. Since the ends of the cells actually contact the supported body, it is desirable to have the cells arranged quite closely for this enables the ends of the cells to resemble a generally continuous surface. Perhaps the most refined air cell cushions currently available are fabricated in rubber via a dipping process and are disclosed in U.S. Pat. Nos. 3,870,450, 4,005,236 and 4,541,136. To facilitate the dipping and assembly process, the air cells of these cushions have a fluted configuration, each with a number of fins, so that when the cells are inflated they will expand laterally into contact with each other and their ends will collectively form a generally uniform supporting surface, even though they are separated mechanically to provide a wide gluing surface at their base.
These cushions provide uniform load supporting characteristics, but are difficult and expensive to manufacture, owing primarily to the large number of fins in each cell and to the fact they are dip molded from latex involving an expensive process. The dip molding and resultant fabrication of the cushion is an expensive labor intensive process which requires gluing a backing sheet to the cellular sheet while still maintaining the interconnecting open air passages between adjacent cells. Also, sensitivity allergic reactions to latex is much more prevalent than once was expected. Thus, an alternative to latex as a cushion cell material is desirable, even though latex cushion cells can be covered with neutral covers. The covers, however, tend to degrade the displacement and force equalization characteristics of the resultant cushion.